The invention relates generally to shock simulation apparatus and methods for testing any industry hardware, component(s) or subsystem(s), electronic or otherwise. More particularly, the invention relates to utilizing formed explosive charges mounted on a test plate which completely or partially sever a portion of the plate, or penetrate a part of the plate, to simulate pyroshock test conditions, which are efficient, repeatable and with less damage to the test plate.
Components and subsystems of larger systems exposed to environments which are generated by explosives or explosive events are often subjected to pyroshock testing to prove they can survive in the actual application. Components typical of aerospace systems are often subjected to pyroshock events during powered flight or field deployment. Explosive devices such as linear shaped charges, flexible linear shaped charges, or mild detonating fuse, may produce these shock events. Additionally, components may also be subjected to complex shocks that travel through multiple structures as a result of an explosive event. As a result, system components and subsystems must be qualified for these environments which often include required margins, which typically are 6 dB, or double the actual environment. Due to the high cost and complexity of most aerospace systems, component qualification using the actual pyroshock environment on full scale assemblies is not practical, and would not produce the required margins. For this reason, laboratory simulations of shock environments are conducted on individual components and subassemblies. Over the years, the ability to measure the actual shock environment, both in flight and during ground tests, has become increasingly better as analytical measurement technologies have improved. Because of this, as well as having to include required margins, the aerospace industry demands improved shock testing capability. This has driven test labs to provide increasingly higher shock magnitudes with more precision, predictability and repeatability.
Traditionally, pyroshock simulation has been performed using varying lengths (typically 5-50 feet) of detonating cord taped in place and initiated with a blasting cap. For example, in one known system, a smaller plate, or ‘shelf’, is attached (typically welded) to the larger test plate which is typically 0.5 inch to 1 inch thick. One or more test item(s) is mounted on the shelf and an explosive charge is affixed on the back side of the test plate. Elastic cords or chains suspend this entire system vertically i.e., so that the primary plane of the test plate is vertical. Detonation of the explosives subjects the test item to the resulting shock stimulus, which are measured by one or more accelerometers mounted either directly on the test plate or on the shelf or on the test item(s). In another known system, a test plate is suspended horizontally i.e., so that it's primary plane is horizontal, and one or more test item(s) are mounted directly on this test plate. The explosive is affixed either on the bottom side of the test plate or along the perimeter edge of the test plate. The test item is subjected to the shock stimulus resulting from detonation of the explosive charge, which is measured by accelerometers mounted on the plate or the test item(s).
An increasing number of applications within the aerospace industry are requiring shock simulations to meet shock magnitudes of 30,000 to 60,000 g's, or more. Using the above-described traditional methods to generate shocks of this magnitude can cause large deformations to the test plate and subsequent damage to the test item(s) and their mounting configurations (e.g. shelves) that interface to the test plate. The damage to the test plate can also disrupt the plate's mechanical properties, which complicates test repeatability within the specified tolerance bands. Consequently, test plates have to be frequently replaced (or repaired) and the test apparatus must be re-calibrated prior to each subsequent use, which increases cost and can cause schedule delays.
Additionally, the test facility may be only able to withstand a certain level of net explosive weight (NEW) that is fired to generate each shock. In one of the previous examples, in order to generate a 30,000 g minimum shock magnitude, 40 ft of 50 grains/foot (gr/ft) detonating cord was used. This results in firing a little over a quarter pound of explosives (129 grams) for each shock. For explosive weights of this magnitude to be repeatedly fired, structural capabilities, safety, and survivability of the facility must be strongly considered.